1 Department of
Psychiatry and Behavioural Sciences, The University of Western Australia,
Australia2 School of Psychology,
The University of Queensland, Australia3 The University of Sydney,
Australia4 Department of Psychology,
The University of Western Australia, Australia5 Department of Pharmacology,
The University of Western Australia, Australia

A dissociation between two putative
measures of resource allocation, electrodermal orienting and secondary
task reaction time (RT), has been observed during a discrimination and
counting task. The anomalous finding of this dissociation effect, secondary
task RT, was investigated by varying the nature of the counting task. Participants
(N = 24) were presented with circle and ellipse shapes. Group Count was
asked to count how many times one shape was presented (task-relevant) and
ignore all presentations of another shape (task-irrelevant). Group Longer
was asked to count the number of longer-than-usual presentations of the
task-relevant shape and ignore the task-irrelevant shape. Concurrent with
the counting task, each group performed a RT task to an auditory probe.
Secondary RT at probe positions of 50, 150, and 250 ms following shape
onset was slower during task-irrelevant shapes than during task-relevant
shapes. Secondary RT also showed at downward parallel trend across probe
positions for each shape. These results did not differ between groups.
The RT data are interpreted as reflecting a serial processing mechanism,
not a resource limited mechanism, thus providing an explanation of the
dissociation effect. The implications for resource allocation models or
orienting and research on human workload interactions are discussed.